1. Field of the Invention
The present invention relates to a fuel injection amount control system for a diesel engine to control a fuel injection amount electrically by an electronic-hydraulic governor.
2. Description of the Related Art
In recent years, a fuel injection amount control system for a diesel engine to control a fuel injection amount electrically by an electronic-hydraulic governor instead of a mechanical-hydraulic one has widely been used in vehicles.
Such a fuel injection amount control system collects into a control unit an engine driving condition and a driver's operating condition as information signals detected by an engine speed sensor and an acceleration sensor and controls the electronic-hydraulic governor based on the control signals from the control unit. As shown in FIG. 4, the electronic-hydraulic governor 1 comprises a DC linear motor 3 operated by the signals from the control unit, a control rack 5 engaging with the plunger in a fuel injection pump body which is not shown, a link 7 transmitting the activation of the DC linear motor 3 to the control rack 5, and a rack sensor 9 detecting the position of the control rack 5.
And, the fuel injection amount is adjusted by revolving the plunger in the fuel injection pump body by the control rack 5. The control unit calculating the necessary amount of fuel injection based on the information signals detected by the acceleration sensor and the engine speed sensor and the target rack position based on the fuel injection amount (the position of control rack 5 which is adequate in relation to the calculated amount of the fuel injection), changes the value of electrical current to the DC linear motor 3 in order that the target rack position coincides with the real rack position (the real position of the control rack 5 which is transferred by the DC linear motor 3), and controls the position of the control rack 5.
Usually in such a fuel injection amount control system, the fuel injection amount when fully accelerated is determined for each engine speed in advance, and the position of the control rack 5 for deciding the fuel injection amount is generally called the "full-rack position".
FIG. 5 is an example showing the full-rack position set up for each engine speed. The full-rack position at 1,000 rpm in engine speed, for example, indicates 12.00 mm. Then the control unit controls the DC linear motor 3 based on the value detected by the rack sensor 9 and transfers the control rack 5 from the standstill position(=0.00 mm) to 12.00 mm.
Thus, the prescribed fuel injection amount can be brought by revolution of the plunger according to the position of the control rack 5.
But, when a driver, driving at 1,000 rpm in engine speed and 40% in acceleration (point A in FIG. 5), suddenly and vigorously steps on the accelerator in order to pass another car ahead and the engine speed reaches 2,000 rpm, the DC linear motor 3 transfers the control rack 5 to the full-rack position (point B in FIG. 5) to bring the corresponding fuel injection amount. In that case, if the target position of rack L which is the difference from the point A to B is large, it has a disadvantage that the control rack 5 overshoots by inertia to bring the excess amount of the fuel injection, which causes black smoke by the worse effect of combustion.